1. Field of the Invention
The present invention relates to a communication device, an edge device and a packet forwarding method. The present invention relates to a technology schemed to enhance and increase an efficiency of services of MPLS (Multi protocol Label Switching) utilized as a backbone technology for IP-VPN (Internet Protocol-Virtual Private Network) services provided by carriers and also utilized for configuring the VPN on MAN (Metropolitan Area Network) over the recent years.
2. Description of the Related Art
The IP-VPN is capable of easily configuring a multipoint-to-multipoint network in a fee system that does not depend on the distance. Therefore, not only new users but also the users having utilized the conventional leased lines so far come to utilize the IP-VPN, and a sharp rise in demand for the IP-VPN can be seen.
Further, there will be a demand for the MPLS for configuring a high-speed and secure network when introducing a local information highway with a shift to the electronic government. To give a deeper insight, if the cost for the introduction of the MPLS decreases by a spread of the MPLS, it can be considered that the MPLS is applied to an intra-office LAN (Local Area Network).
In the case of exemplifying the IP-VPN services having the largest influence on activating the MPLS market, the MPLS can be provided to end users simply by introducing the MPLS into a carrier backbone (core network) without having any influence on the existing access circuits and use communication devices.
The carriers initially did not provide network services being able to understand the IP (Internet Protocol). The mass of traffics of the users become, however, the IP by the spread of the Internet, and traffic size (quantity) rises skywards. Paying the attention to this tendency, the carriers schemed to incorporate the IP routing function into the networks. Then, the carriers put a focus on the MPLS from which to yield effects by an intensive investment into the core network.
According to the MPLS, routing information obtained by operating a routing protocol (such as RIP (routing Information Protocol), OSPF (Open Shortest Path First), BGP (Border Gateway protocol) on the network layer, is assigned as a “label” having a short fixed length to a physical link between MPLS devices.
The label is similar to VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) in ATM (A synchronous Transfer Mode) and can be treated as if a connection between arbitrary networks (according to the MPLS, this connection is called LSP (Label Switched Path)). Accordingly, the MPLS is capable of enhancing the forwarding performance and easily managing the traffic as by the ATM.
At the present, network resources of the carriers are sufficient for the user's traffic quantity, and hence a load (cost) on the communication facilities of the carriers does not become excessive. In the future, however, there might arise an anxiety for an increase in the load especially upon the edge devices actualizing a large proportion of the functions of the MPLS.
The edge devices actualize roughly two functions. One function is a function of converging and integrating a variety of access circuits. Another function is an MPLS function provided within the MPLS domain. The former functions, as a matter of course, give a direct influence to the increase in the load upon the edge device. The latter MPLS function is categorized as hardware (device) in the MPLS domain into an edge device (edge node) and a label switching router (LSR).
The functions of the LSR are simplified in its function for gaining a higher speed. The LSR performs both of operations (a label assignment and so on) related to the routing protocol and LDP (Label Distribution Protocol), and label switching (forwarding).
On the other hand, the edge device needs, in addition of the operations based on the routing protocol and the LDP and the IP address based packet forwarding process of the IP packet based on the IP address, attach and remove the label used in the MPLS domain to and from the packet, and perform label switching and priority control and the like.
FIG. 10 shows conventional MPLS functions sharing. As shown in FIG. 10, an edge device located in backbone of a carrier network terminates a MPLS domain. Hence, as a matter of course, the label is unable to be recognized outside the MPLS domain.
Referring to FIG. 10, an edge device (entrance edge device) corresponding to an entrance of the MPLS domain (receiving the packet from a communication device of users side (user communication device)) receives the IP packet from the user communication device as a sender (transmitting side), and searches for an entry matching with a destination IP address from a routing table in the same algorithm as the normal IP routing.
In the MPLS domain, the label is determined for every routing entry on the basis of the LDP and the like, and the edge device recognizes the label from a result of the search and pads (attaches; inserts) the label to the IP packet. Then, this labeled packet is forwarded into the MPLS domain.
Each of the LSRs receives the IP packet and performs forwarding based on the label (label switching). Thus, the IP packet is transferred (across the LSRs) to the edge device (exit edge device) that is an exit of the MPLS domain. The exit (egress) edge device removes the label from the IP packet, and the IP packet is transferred to the user communication device as a receiver on the basis of the destination IP address.
Normally, an access circuit interface (which is a UNI (User-Network Interface) between the user communication device and the edge device in FIG. 10) accommodating the user, has no routing function on the layer 3 (network layer), and there is carried out a point-to-point transmission of the IP packet on the layer 2 (data link layer) or thereunder.
As explained above, the edge devices are given large shares of roles in the MPLS. Especially the entrance edge device (in the prior art) that forwards the packet into the MPLS domain from the user communication device, must executes steps such as invariably referring to the destination IP addresses of all the IP packets, searching the routing table, attaching the labels and forwarding the IP packets to the output port.
The edge device is incapable of performing label switching during a packet flow from the user communication device into the MPLS domain, and therefore an enhanced forwarding performance can not be expected during this flow. According to the prior art, only the LSRs excluding the edge devices in the MPLS domain are given a label switching capability.
Further, the edge devices often take such a form that plural types of access circuits accommodate a tremendous number of user communication devices, and a more strict user management is demanded of IP-VPN and so on. It is therefore clear that the performance of the edge device becomes a bottleneck when viewed from an end-to-end architecture (application).